Tcl Built-In Commands package(1T)
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NAME
package - Facilities for package loading and version control
SYNOPSIS
package forget ?package package ...?
package ifneeded package version ?script?
package names
package present ?-exact? package ?version?
package provide package ?version?
package require ?-exact? package ?version?
package unknown ?command?
package vcompare version1 version2
package versions package
package vsatisfies version1 version2
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DESCRIPTION
This command keeps a simple database of the packages avail-
able for use by the current interpreter and how to load them into the interpreter. It supports multiple versions of eachpackage and arranges for the correct version of a package to
be loaded based on what is needed by the application. Thiscommand also detects and reports version clashes. Typi-
cally, only the package require and package provide commands
are invoked in normal Tcl scripts; the other commands areused primarily by system scripts that maintain the package
database.The behavior of the package command is determined by its
first argument. The following forms are permitted:package forget ?package package ...?
Removes all information about each specified package
from this interpreter, including information providedby both package ifneeded and package provide.
package ifneeded package version ?script?
This command typically appears only in system confi-
guration scripts to set up the package database. It
indicates that a particular version of a particularpackage is available if needed, and that the package
can be added to the interpreter by executing script. The script is saved in a database for use by subsequentpackage require commands; typically, script sets up
auto-loading for the commands in the package (or calls
load and/or source directly), then invokes package pro-
vide to indicate that the package is present. There
may be information in the database for several dif-
ferent versions of a single package. If the database
Tcl Last change: 7.5 1Tcl Built-In Commands package(1T)
already contains information for package and version,
the new script replaces the existing one. If thescript argument is omitted, the current script for ver-
sion version of package package is returned, or an
empty string if no package ifneeded command has been
invoked for this package and version.
package names
Returns a list of the names of all packages in the
interpreter for which a version has been provided (viapackage provide) or for which a package ifneeded script
is available. The order of elements in the list is arbitrary.package present ?-exact? package ?version?
This command is equivalent to package require except
that it does not try and load the package if it is not
already loaded.package provide package ?version?
This command is invoked to indicate that version ver-
sion of package package is now present in the inter-
preter. It is typically invoked once as part of anifneeded script, and again by the package itself when
it is finally loaded. An error occurs if a differentversion of package has been provided by a previous
package provide command. If the version argument is
omitted, then the command returns the version number that is currently provided, or an empty string if nopackage provide command has been invoked for package in
this interpreter.package require ?-exact? package ?version?
This command is typically invoked by Tcl code that wishes to use a particular version of a particularpackage. The arguments indicate which package is
wanted, and the command ensures that a suitable versionof the package is loaded into the interpreter. If the
command succeeds, it returns the version number that is loaded; otherwise it generates an error. If both the-exact switch and the version argument are specified
then only the given version is acceptable. If -exact
is omitted but version is specified, then versions later than version are also acceptable as long as they have the same major version number as version. If both-exact and version are omitted then any version whatso-
ever is acceptable. If a version of package has
already been provided (by invoking the package provide
command), then its version number must satisfy the cri-
teria given by -exact and version and the command
returns immediately. Otherwise, the command searches the database of information provided by previous Tcl Last change: 7.5 2Tcl Built-In Commands package(1T)
package ifneeded commands to see if an acceptable ver-
sion of the package is available. If so, the script
for the highest acceptable version number is evaluatedin the global namespace; it must do whatever is neces-
sary to load the package, including calling package
provide for the package. If the package ifneeded data-
base does not contain an acceptable version of thepackage and a package unknown command has been speci-
fied for the interpreter then that command is evaluated in the global namespace; when it completes, Tcl checksagain to see if the package is now provided or if there
is a package ifneeded script for it. If all of these
steps fail to provide an acceptable version of thepackage, then the command returns an error.
package unknown ?command?
This command supplies a ``last resort'' command toinvoke during package require if no suitable version of
a package can be found in the package ifneeded data-
base. If the command argument is supplied, it contains the first part of a command; when the command isinvoked during a package require command, Tcl appends
two additional arguments giving the desired package
name and version. For example, if command is foo barand later the command package require test 2.4 is
invoked, then Tcl will execute the command foo bar test2.4 to load the package. If no version number is sup-
plied to the package require command, then the version
argument for the invoked command will be an emptystring. If the package unknown command is invoked
without a command argument, then the current package
unknown script is returned, or an empty string if there is none. If command is specified as an empty string,then the current package unknown script is removed, if
there is one.package vcompare version1 version2
Compares the two version numbers given by version1 andversion2. Returns -1 if version1 is an earlier version
than version2, 0 if they are equal, and 1 if version1 is later than version2.package versions package
Returns a list of all the version numbers of package
for which information has been provided by package
ifneeded commands.package vsatisfies version1 version2
Returns 1 if scripts written for version2 will work unchanged with version1 (i.e. version1 is equal to or greater than version2 and they both have the same major version number), 0 otherwise. Tcl Last change: 7.5 3Tcl Built-In Commands package(1T)
VERSION NUMBERS Version numbers consist of one or more decimal numbers separated by dots, such as 2 or 1.162 or 3.1.13.1. The first number is called the major version number. Largernumbers correspond to later versions of a package, with
leftmost numbers having greater significance. For example, version 2.1 is later than 1.3 and version 3.4.6 is laterthan 3.3.5. Missing fields are equivalent to zeroes: ver-
sion 1.3 is the same as version 1.3.0 and 1.3.0.0, so it is earlier than 1.3.1 or 1.3.0.2. A later version number is assumed to be upwards compatible with an earlier version number as long as both versions have the same major version number. For example, Tcl scripts written for version 2.3 ofa package should work unchanged under versions 2.3.2, 2.4,
and 2.5.1. Changes in the major version number signify incompatible changes: if code is written to use version 2.1of a package, it is not guaranteed to work unmodified with
either version 1.7.3 or version 3.1. PACKAGE INDICESThe recommended way to use packages in Tcl is to invoke
package require and package provide commands in scripts, and
use the procedure pkg_mkIndex to create package index files.
Once you've done this, packages will be loaded automatically
in response to package require commands. See the documenta-
tion for pkg_mkIndex for details.
EXAMPLES
To state that a Tcl script requires the Tk and http pack-
ages, put this at the top of the script:package require Tk
package require http
To test to see if the Snack package is available and load if
it is (often useful for optional enhancements to programs where the loss of the functionality is not critical) do this:if {[catch {package require Snack}]} {
# Error thrown - package not found.
# Set up a dummy interface to work around the absence
} else {# We have the package, configure the app to use it
}SEE ALSO
msgcat(1T), packagens(1T), pkgMkIndex(1T)
KEYWORDSpackage, version
Tcl Last change: 7.5 4Tcl Built-In Commands package(1T)
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:_______________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE|
|____________________|__________________|_
| Availability | runtime/tcl-8 |
|____________________|__________________|_
| Interface Stability| Uncommitted ||____________________|_________________|
NOTES Source for Tcl is available on http://opensolaris.org. Tcl Last change: 7.5 5